Cancer
Cancer is one of the most common diseases, and a major cause of death in the western world. In general, incidence rates increase with age for most forms of cancer. As human populations continue to live longer, due to an increase of the general health status, cancer may affect an increasing number of individuals. The cause of most common cancer types is still largely unknown, although there is an increasing body of knowledge providing a link between environmental factors (dietary, tobacco smoke, UV radiation etc) as well as genetic factors (germ line mutations in “cancer genes” such as p53, APC, BRCA1, XP etc) and the risk for development of cancer.
No definition of cancer is entirely satisfactory from a cell biological point of view, despite the fact that cancer is essentially a cellular disease and defined as a transformed cell population with net cell growth and anti-social behavior. Malignant transformation represents the transition to a malignant phenotype based on irreversible genetic alterations. Although this has not been formally proven, malignant transformation is believed to take place in one cell, from which a subsequently developed tumor originates (the “clonality of cancer” dogma). Carcinogenesis is the process by which cancer is generated and is generally accepted to include multiple events that ultimately lead to growth of a malignant tumor. This multi-step process includes several rate-limiting steps, such as addition of mutations and possibly also epigenetic events, leading to formation of cancer following stages of precancerous proliferation. The stepwise changes involve accumulation of errors (mutations) in vital regulatory pathways that determine cell division, asocial behavior and cell death. Each of these changes may provide a selective Darwinian growth advantage compared to surrounding cells, resulting in a net growth of the tumor cell population. A malignant tumor does not only necessarily consist of the transformed tumor cells themselves but also surrounding normal cells which act as a supportive stroma. This recruited cancer stroma consists of connective tissue, blood vessels and various other normal cells, e.g., inflammatory cells, which act in concert to supply the transformed tumor cells with signals necessary for continued tumor growth.
The most common forms of cancer arise in somatic cells and are predominantly of epithelial origin, e.g., prostate, breast, colon, urothelium and skin, followed by cancers originating from the hematopoetic lineage, e.g., leukemia and lymphoma, neuroectoderm, e.g., malignant gliomas, and soft tissue tumors, e.g., sarcomas.
Cancer Diagnostics and Prognostics
Microscopic evaluation of biopsy material from suspected tumors remains the golden standard for cancer diagnostics. To obtain a firm diagnosis, the tumor tissue is fixated in formalin, histo-processed and paraffin embedded. From the resulting paraffin block, tissue sections can be produced and stained using both histochemical, i.e., hematoxylin-eosin staining, and immunohistochemical (IHC) methods. The surgical specimen is then evaluated with pathology techniques, including gross and microscopic analysis. This analysis often forms the basis for assigning a specific diagnosis, i.e., classifying the tumor type and grading the degree of malignancy, of a tumor.
Malignant tumors can be categorized into several stages according to classification schemes specific for each cancer type. The most common classification system for solid tumors is the tumor-node-metastasis (TNM) staging system. The T stage describes the local extent of the primary tumor, i.e., how far the tumor has invaded and imposed growth into surrounding tissues, whereas the N stage and M stage describe how the tumor has developed metastases, with the N stage describing spread of tumor to lymph nodes and the M stage describing growth of tumor in other distant organs. Early stages include: T0-1, N0, M0, representing localized tumors with negative lymph nodes. More advanced stages include: T2-4, N0, M0, localized tumors with more widespread growth and T1-4, N1-3, M0, tumors that have metastasized to lymph nodes and T1-4, N1-3, M1, tumors with a metastasis detected in a distant organ. Staging of tumors is often based on several forms of examination, including surgical, radiological and histopathological analyses. In addition to staging, for most tumor types there is also a classification system to grade the level of malignancy. The grading systems rely on morphological assessment of a tumor tissue sample and are based on the microscopic features found in a given tumor. These grading systems may be based on the degree of differentiation, proliferation and atypical appearance of the tumor cells. Examples of generally employed grading systems include Gleason grading for prostatic carcinomas and the Nottingham Histological Grade (NHG) grading for breast carcinomas.
Accurate staging and grading is crucial for a correct diagnosis and may provide an instrument to predict a prognosis. The diagnostic and prognostic information for a specific tumor subsequently determines an adequate therapeutic strategy for a given cancer patient. A commonly used method, in addition to histochemical staining of tissue sections, to obtain more information regarding a tumor is immunohistochemical staining. IHC allows for the detection of protein expression patterns in tissues and cells using specific antibodies. The use of IHC in clinical diagnostics allows for the detection of immunoreactivity in different cell populations, in addition to the information regarding tissue architecture and cellular morphology that is assessed from the histochemically stained tumor tissue section. IHC can be involved in supporting the accurate diagnosis, including staging and grading, of a primary tumor as well as in the diagnostics of metastases of unknown origin. The most commonly used antibodies in clinical practice today include antibodies against cell type “specific” proteins, e.g., PSA (prostate), MelanA (melanocytes) and Thyroglobulin (thyroid gland), and antibodies recognizing intermediate filaments (epithelial, mesenchymal, glial), cluster of differentiation (CD) antigens (hematopoetic, sub-classification of lympoid cells) and markers of malignant potential, e.g., Ki67 (proliferation), p53 (commonly mutated tumor suppressor gene) and HER-2 (growth factor receptor).
Aside from IHC, the use of in situ hybridization for detecting gene amplification and gene sequencing for mutation analysis are evolving technologies within cancer diagnostics. In addition, global analysis of transcripts, proteins or metabolites adds relevant information. However, most of these analyses still represent basic research and have yet to be evaluated and standardized for the use in clinical medicine.
Malignant Melanoma
Cutaneous malignant melanoma is a malignant tumor derived from melanocytes located in the skin. Every year, about 160,000 new cases of malignant melanoma are diagnosed world wide. In developed countries, survival rates are high (91% in the USA and 81% in Europe), but developing countries have a considerably lower survival rate of only about 40%. Malignant melanoma is a common skin tumor with a rapidly increasing incidence rate, and since it affects a relatively young patient population each melanoma-related death corresponds to approximately 19 years of life lost. The incidence has increased dramatically in Caucasians in the last few decades, and in the Nordic countries there has been an average increase of approximately 30% every 5 years.
The increased incidence in the last decades is partly explained by altered sun exposure habits of the population, but several hereditary risk factors are also known. Other important risk factors are the number of pigment nevi, the number dysplastic nevi, and skin type. An increased risk is coupled to many nevi, both benign and dysplastic, and fair skin. Familial history of malignant melanomas is a risk factor, and approximately 8-12% of malignant melanoma cases are familial.
Malignant Melanoma Diagnostics
Malignant melanomas are clinically recognized based on the ABCD(E) system, where A stands for assymmetry, B for border irregularity; C for color variation, D for diameter >5 mm, and the proposed E for evolving. Further, an excision biopsy is generally performed in order to make a correct diagnosis by microscopic evaluation.
Infiltrative malignant melanoma is traditionally divided into four principal histopathological subgroups: Superficial spreading melanoma (SSM), nodular malignant melanoma (NMM), lentigo maligna melanoma (LMM), and acral lentiginous melanoma (ALM). Approximately 60% of all melanomas belong to the SSM subtype, 20% to the NMM subtype, and 7% to LMM. ALM arises on palmar and plantar skin along with the nails. This subtype is uncommon in Caucasians, but the most common type found in Orientals and black people. Other rare types also exists, such as desmoplastic malignant melanoma.
A substantial subset of malignant melanomas appear to arise from melanocytic nevi and features of dysplastic nevi are often found in the vicinity of infiltrative melanomas. Melanoma is thought to arise through stages of progression from normal melanocytes or nevus cells through a dysplastic nevus stage and further to an in situ stage before becoming invasive. Some of the subtypes evolve through different phases of tumor progression, which are called radial growth phase (RGP) and vertical growth phase (VGP).
Malignant melanomas are staged according to the American Joint Committee on Cancer (AJCC) TNM-classification system, where Clark level (see below) is considered in T-classification. Stages I and II represent no mestastatic disease and for stage I (T1a/b-2a,N0,M0) prognosis is very good. The 5-year survival for stage I disease is 90-95%, for stage II (T2b-4-b,N0,M0) the corresponding survival rate ranges from 80 to 45%. Stages III (T1a-4-b,N1a-3,M0) and IV (T(aII),N(aII),M1a-c) represent spread disease, and for these stages 5-year survival rates range from 70 to 24%, and from 19 to 7%, respectively. Clark level is the level of tumour invasion into normal skin, and this level has been shown to be a prognostic factor (see below). Clark levels ranges from I to V.
When the primary tumor has a thickness of >1 mm, ulceration, or Clark level IV-V, sentinel node biopsy (SNB) is performed. SNB is performed by identifying the first draining lymph node/s (i.e the SN) from the tumour. This is normally done by injection of radiolabelled colliod particles in the area around the tumour, followed by injection of Vital Blue dye. Close to 100% of all sentinel nodes are detected by this method. Rather than dissection of all regional lymph nodes, which was the earlier standard procedure, only the sentinel nodes are then removed and carefully examined. Following complete lymph node dissection is only performed in confirmed positive cases.
The histopathological features of malignant melanomas vary widely and therefore immunohistochemistry is often used to distinguish malignant melanoma from other tumor forms. Traditionally, S-100 has been used as an immunohistochemical marker of melanocytes, but this protein also stains positive in e.g. Langerhans cells and nerve fibers. Other markers like Melan-A (MART-1), HMB45, and tyrosinase can stain melanocytes more specifically, but since they lack the sensitivity of S100, a combination of S100 with melanocytic markers is often used. In addition to markers of differentiation, proliferation markers may also be used in the differential diagnostics of melanocytic lesions with uncertain malignant potential. The most accepted markers for cells active in the cell cycle are antibodies binding to Ki-67, and frequency of Ki-67 positive melanocytic cells is generally used to distinguish a malignant lesion from benign variants.
Treatment of Malignant Melanoma
Today, the primary treatment of malignant melanoma is radical surgery. Even though survival rates are high after excision of the primary tumour, melanomas tend to metastasize relatively early, and for patients with metastatic melanoma the prognosis is poor, with a 5-year survival rate of less than 10%. Radical removal of distant metastases with surgery can be an option and systemic chemotherapy can be applied, but response rates are normally low (in most cases less than 20%), and most treatment regiments fail to prolong overall survival.
The first FDA-approved chemotherapeutic agent for treatment of metastatic melanoma was dacarbazine (DTIC), which can give response rates of approximately 20%, but where less than 5% may be complete responses. Temozolamid is an analog of DTIC that has the advantage of oral administration, and which have been shown to give a similar response as DTIC. Other chemotherapeutic agents, for example different nitrosureas, cisplatin, carboplatin, and vinca alkaloids, have been used, but without any increase in response rates.
The failure of single chemotherapeutic agents to show effect against metastatic melanomas has led to several clinical trials of multi-drug combinations, but no advantage over treatment with DTIC alone may be stated.
Since chemotherapy is an inefficient treatment method, immunotherapy agents have also been proposed. Most studied are interferon-alpha (IFN-α) and interleukin-2 (IL-2). As single agents they have not been shown to give a better response than conventional treatment, but in combination with chemotherapeutic agents higher response rates have been reported. Radiation treatment may be given as an adjuvant after removal of lymphatic metastases, but malignant melanomas are relatively radioresistant. Radiation treatment might also be used as palliative treatment.
Studies have shown that BRAF mutations are common in both primary and metastatic melanomas, these mutations are reported to be present in 50-70% of all melanomas. This has led to an interest in B-raf inhibitors, such as Sorafenib, as therapeutic agents but routine treatment with such substances are still far ahead.
Prognostics and Treatment Predictive Factors
Patients whom are diagnosed at an advanced stage with metastases generally have a poor prognosis. For patients diagnosed with a localized disease the most important prognostic indicator is the thickness of the tumor measured in mm (Breslow) followed by ulceration. Clark level is important for thin lesions (<1 mm). Other prognostic factors include age, anatomic site of the primary tumor and gender. In Sweden, the 5-year melanoma specific survival rate is 98% for patients in stage IA and 49% for patients in stage IVB. For metastatic melanoma, the number of positive lymph nodes are of importance as well as if the metastases are macro- or microscopic. The sentinel node (SN) status may be a very important prognostic factor, and the 5-year survival of SN-negative patients has been shown to be as high as 90%.
The only serum biomarker included in the AJCC staging system for melanoma, is Lactate dehydrogenase (LDH), which is a marker for disease progression. Patients with distant metastases and elevated LDH levels belong to stage IV M1c. Another serum biomarker of interest is S100B. High S100B levels are associated with disease progression, and a decrease in the S100B level is an indicator of treatment response. Melanoma-inhibiting activity (MIA) is yet another serum biomarker that has been evaluated regarding its prognostic value. Studies have shown that elevated MIA levels are rare in stage I and II disease, whereas in stage III or IV, elevation in MIA levels can be seen in 60-100% of cases.
Some tissue biomarkers that have been identified through tissue microarray studies are RGS1 (associated with reduced relapse-free survival (RFS)), Osteopontin (associated with both reduced RFS and disease-specific survival (DSS), and predictive of SLN metastases), HER3 (associated with reduced survival), and NCOA3 (associated with poor RFS and DSS, and predictive of SLN metastases). However, all these need to be further validated.
Endpoint Analysis
Endpoint analysis for trials with adjuvant treatments for cancer gives important information on how the patients respond to a certain therapy. Overall survival (OS) has long been considered the standard primary endpoint. OS takes in to account time to death, irrespective of cause, e.g. if the death is due to cancer or not. Loss to follow-up is censored and regional recurrence, distant metastases, second primary malignant melanomas and second other primary cancers are ignored.
Today, an increasing number of effective treatments available for many types of cancer have resulted in the need for surrogate endpoints to allow for a better evaluation of the effect of adjuvant treatments. Partly due to the long follow-up period required to demonstrate that adjuvant treatments improve OS, this endpoint is often complemented with other clinical endpoints that give an earlier indication on how successful the treatment is.
In the present disclosure, one surrogate endpoint was used, namely disease-free survival (DFS). Analysis of DFS includes time to any event related to the same cancer, i.e. all cancer recurrences and deaths from the same cancer are events.